In continuous ink jet printing, electrically conductive ink is supplied under pressure to a region that distributes the ink via a plurality of orifices, typically arranged in a linear array. The ink discharges from the orifices, forming a jet array, which breaks into droplet streams. Individual ink droplets in the droplet streams are selectively charged by a drop charging assembly, which deflects the drops from their normal trajectories. The deflected drops may be caught and recirculated. The undeflected drops are allowed to proceed to a print medium forming an image.
Drops are typically charged by a drop charging assembly having a plurality of charging electrodes along one edge, and a corresponding plurality of connecting leads along one of the faces. The edge of the drop charging assembly, having charging electrodes, is placed in close proximity to the ink droplet stream. Charges are applied to the leads to induce charges in the drops as they break off from the jet array.
Uniformity of drop charge is essential in continuous ink jet printheads utilizing planar electrode structures. These printheads require a substantial difference in charge for the “catch drops” compared to the “print drops”. Drops with a high charge are attracted towards a catcher and recycled. Drops with a low charge are printed on print media. Print quality defects are introduced if the charge on the print drops is excessive or uncontrolled. Nominal charge level on the print drops varies in each printhead design.
Pipkorn U.S. Pat. No. 4,622,562 teaches that a charge plate for a printhead must be heated to prevent the formation of condensate, see also, Wood U.S. Pat. No. 4,928,116. The prior art described herein are incorporated by reference.
A need exists to improve print quality with a better drop charging assembly, in particular, for print stations with arrays longer than 4 inches.
The present embodiments described herein were designed to meet these needs.